What if I say there is a material that could become the world’s most powerful rocket fuel with a specific energy twenty times that of the Space Shuttle’s engines? Or that this same material could become the first substance in the world to exhibit superconducting properties at room temperature, and that if this technology is implemented, it will be such a giant step forward that computers will become thousands of times more powerful than today? This breakthrough will help us finally realize the age-old dream of mankind about nuclear power. The use of such a material would not only make current power plants safer and more efficient, but would also completely transform industries such as medicine and transportation. For the first time, a hypothesis about the possibility of the existence of such a substance was put forward back in 1935. And since then, scientists, sparing no time and effort, have been trying to pave the way for its creation. Today we may be one step closer to creating such a substance.
Everything, as always and everywhere, starts with hydrogen. Hydrogen permeates the entire Universe. It is the most common of all chemical elements – its molecule consists of only one proton and one electron. However, if hydrogen in the gaseous state is an elementary simple substance, then during the transition from one state to another its complexity increases many times over. Proof of this is the colossal rotating formation, 8,000 miles in diameter, located below Jupiter’s cloud tops – the largest ocean in the solar system. The pressure generated in the depths of the planet is sufficient to break the bonds between protons and electrons and transfer the element to a new unusual state: not into plasma, not into gas, but into liquid metallic hydrogen.
The key word here is metal… The 1935 theory predicted that at a sufficiently high pressure, hydrogen would exhibit the properties of a metal, as the molecules disintegrate into their constituent parts, turning into an electrical conductor. Metals are also characterized by a pronounced luster and strength, in other words, ordinary transparent hydrogen gas will become opaque.
But what distinguishes metallic hydrogen, for example, from molten gold? The difference is that metals have a lattice at the atomic level. The lattice is formed from ions surrounded by freely moving electrons. Metallic hydrogen is unable to form such a lattice, since hydrogen has nothing but one proton, and therefore does not have enough constituent particles to form a lattice. And it is for this reason that metallic hydrogen acquires many unique properties.
It is believed that hydrogen in the metallic state can be metastable, in other words, it remains metallic even when the pressure drops to normal levels. The picture resembles the one when, in order to turn carbon into diamond, you need to apply tremendous pressure, but if the pressure is removed after that, the diamond will not turn back into carbon, but will remain a diamond. However, in practice, we cannot yet verify the metastability of metallic hydrogen, since there are no samples of metallic hydrogen on Earth. True, at one time a group of scientists from Harvard claimed that they managed to create such a substance in the laboratory, but the sought-for sample disappeared before further analysis could be carried out. Needless to say, the claims made by these scientists should be taken very critically.
However, last year in the magazine Nature results were published new, more promising research…
Initially, the research team set about experimenting by applying a small pressure (measured in gigapascals, GPa) to a dense hydrogen sample. The hydrogen remained transparent in both the visible and infrared spectrum. As mentioned above, the distinctive features of metals are their luster and opacity. However, when the pressure was increased to 300 GPa, the sample ceased to be transparent in the visible spectrum. Then the pressure on the sample was gradually increased to 400 GPa and above, that is, 4 million times more than the Earth’s atmospheric pressure. When the pressure increased to 425 GPa, the sample was no longer transparent in the infrared spectrum. Hydrogen began to reflect light, that is, it received a new property, and this led the researchers to believe that a sample of dense hydrogen passed into the long-awaited metallic state.
The phase shift of the sample was reversible, although the researchers are not confident that hydrogen would retain its metallic properties at pressures above 425 GPa. Using existing technologies, it is practically impossible to measure the properties of hydrogen samples under extreme conditions (for example, under high pressures or at low temperatures). For this reason, the researchers were also unable to measure the conductivity of the sample – the results of such measurements could provide irrefutable evidence of the presence of metallic hydrogen. Even computational methods that predict the pressure values at which hydrogen transforms into a metallic state cannot be considered accurate, since we cannot put the necessary corrections at the quantum level into the computer model.
Nevertheless, this study can be regarded as the best evidence that hydrogen is capable of transforming into a metallic state. If scientists really succeed in creating metallic hydrogen, such a substance will appear on our planet for the first time in its history. And this can happen even during our lifetime.
The main problems to be solved will relate to the measurement of the parameters of electrical conductivity and resistance of metallic hydrogen. This will help to understand whether this element will be able to fulfill its potential and, possibly, become one of the most valuable substances on Earth.
It would be ideal to use metallic hydrogen as a rocket fuel, since it is light and takes up small volume. Converting metallic hydrogen back to molecular hydrogen would release a tremendous amount of energy, comparable to the energy originally required to create metallic hydrogen, and that would turn metallic hydrogen into a super-powerful fuel that could revolutionize rocketry. By comparison, the specific impulse (a measure of how quickly propellant is ejected from the back of a spacecraft, as well as the efficiency of a space projectile) of currently used rockets is about 450 seconds. The specific impulse of rockets using metallic hydrogen is estimated at 1,700 seconds. In other words, the rockets launched into orbit will be able to have not two stages, but only one, which will significantly increase the payload of the rockets.
Thus, the use of metallic hydrogen will allow us to more confidently explore neighboring worlds and at the same time provide long-awaited progress on our own planet – new technologies for storing and transferring energy will be developed, and the devices we use in our daily life will undergo dramatic changes. And, if research like last year continues, the theoretical possibility creation metallic hydrogen will become practical. This discovery may become one of the most important in the entire history of mankind.
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